A compact is polycrystalline mass of abrasive particles (e.g., diamond and cubic boron nitride) bonded together to form an integral, tough, coherent, high-strength mass. Representative U.S. Pat. Nos. on the subject of diamond compacts are: 3,136,615 (boron carbide bonding medium); 3,141,746; 3,239,321 (graphite-free diamond compact); 3,744,982 (boron alloyed diamond compact process): 3,816,085; and 3,913,280. A composite compact is a compact bonded to substrate material, such as cemented tungsten carbide (see U.S. Pat. No. 3,745,623) which is hereby incorporated by reference.
Compact cutting tools made from polycrystalline diamond which has been grown from graphite are disclosed in U.S. Pat. No. 3,850,053. Diamond compacts made from diamond mixed with graphite are disclosed in U.S. Pat. No. 3,850,591, and the growth of diamond on a seed crystal is found in U.S. Pat. No. 3,297,407. U.S. Pat. No. 4,164,527 teaches making a superhard article from a briquette made of diamond and a hard alloy matrix encased in an external envelope having a higher contraction coefficient than the briquette.
U.S. Pat. Nos. 3,831,428; (which is hereby incorporated by reference) 4,129,052; and 4,144,739 disclose wire drawing dies made from diamond. A diamond wire die compact in general comprises an inner mass which is predominantly polycrystalline diamond and an outer annular ring of metal bonded carbide bonded to and surrounding the inner mass of symetrical support thereof. The metal bonded carbide mass is selected from the group consisting of tungsten carbide, titanium carbide tantalum carbide and mixtures thereof with metal bonding material therein being present in a quantity of from about 6-25 weight percent and selected from the group consisting of cobalt, nickel, iron and mixtures thereof.
Drill bits utilizing compact cutter elements are disclosed in the following U.S. Pat. Nos. 3,407,445; 3,938,599; 4,006,788; 4,073,354; 4,098,362 (crown made of metal powder and braze alloy); 4,109,737 (compact cutters with tapered pins fitted into recesses); and 4,156,329 (furnace brazing).
The following U.S. patent applications are related to the same subject: Ser. No. 888,259; filed Mar. 20, 1978; and now allowed (sintered metal body with cutters at positive rake angle); Ser. No. 899,767; filed Apr. 24, 1978 and Ser. No. 947,865; filed Oct. 2, 1978 (V-shaped cutter for drag bits); and application Ser. No. 95,902 by Philippe Douglas St. Pierre filed Nov. 19, 1979 and assigned to the same assignee.
Most prior art attempts to use diamond compacts in drill bit applications utilize compacts in the form of right circular cylinders with a thin layer of polycrystalline daimond bonded to a cemented carbide substrate. The cutting element is formed by attaching the compact to the drill bit by brazing or soldering the carbide substrate to a cemented carbide pin which is inserted into sockets in the drill crown. The diamond layer is generally oriented in a radial sense to the center of rotation of the drill bit and penetrates the rock essentially as a cutting tool, with rake angles essentially zero to about five degrees negative. In the design, the cutting elements protrude from the drill bit body, and thereby provide aggressive cutting action. The stresses on each cutting element are severe, and failures occur by gross chipping or cracking of the compact. The failure problem is essentially due to lack of support for the polycrystalline diamond layer which has a shear or tensile strength of only about 100 Kg/mm.sup.2.